For decades, Missouri executions played out in similar fashion: An inmate was strapped to a gurney in a drab room, alone except for the eyes of witnesses staring through thick glass as unidentified executioners administered the lethal chemical from behind a cinderblock wall.

A Missouri inmate has been put to death for a 2003 killing, becoming what is believed to be the first transgender woman executed in the U.S. Amber McLaughlin was put to death Tuesday night, hours after Republican Gov. Mike Parson declined a clemency request.

Unless Missouri Gov. Mike Parson grants clemency, Amber McLaughlin will become the first openly transgender woman executed in the U.S. She is scheduled to die by injection Tuesday for killing a former girlfriend in 2003.

The first openly transgender woman set to be executed in the U.S. is asking Missouri’s governor for mercy.